High-frequency glue curing press



Aug. 25, 1953 H. RE-NN 2,649,877

u HIGH-FREQUENCY GLUE CURING PRESS Filed Aug. 28, 1950 2 Sheets-Sheet l #vz/ENTDR HARRL L RENN EMMJM Traa/vis;

Aug. Z5, 1953 H. RENN HIGH-FREQUENCY GLUE CURING PRESS Filed Aug. 28, 1950 2 Sheets-Sheet 2 #vz/5N TDR HARM-LL RENN TTD RAL/ Patented Aug. 25, 1953 HIGH-FREQUENCY GLUE CURING PRESS Harrell Renn, Albany, Oreg., assignor to M and M Wood Working Company, Portland, Oreg., a corporation of Oregon Application August 28, 1950, Serial N o. 181,776

(Cl. 14A-281) 9 Claims.

This invention relates to an improved apparatus for applying heat and pressure to a glued joint, as, for example, in the patching of plywood where defects have been removed.

In the heat setting of plywood patches by the use of high frequency electrical fields, considerable difficulty has been encountered in developing a satisfactory electrode carrying pressure member to hold the patch in place and establish the necessary high frequency dielectric eld to heat-set the glue on the patch. It has not been possible to nd a dielectric material to insulate the electrodes at the work engaging face of the pressure member which will give satisfactory service under the pressure, electrical and temperature conditions which are necessary toset the patch quickly. It is found that dielectric material on the work engaging face becomes heated to a rather high degree when glue is squeezed out of the joint around the edges of the patch in contact with the dielectric material. Such glue, together with dust and other foreign material, forms a conducting film on the face of the dielectric member Which is heated by the high frequency eld in the same manner as the glue line under the patch. The resulting local heating on the surface of the pressure member not only deteriorates the dielectric material and materially -shortens its life, but it also reduces the heating effect in the glue line under the patch and is wasteful of electrical energy. Also, a flash is liable to occur which forms a carbon path for the electrical current on the surface of the insulating material. This has to be cleaned off before the head will operate satisfactorily. If enough insulating material is placed between the glue line and the metal feet of the head to eliminate this flashing, the power -available to the glue line is decreased and the time necessary to set the patch is increased.

The general object of the present invention is, therefore, to provide an improved pressure member for .a glue curing press, in which the necessary solid dielectric material for insulating the electrodes 4does not come into contact with the Work surface and any glue or dust that might be on such surface. A more particular object is to provide a pressure member having bare metal electrodes to contact the Work directly, wherein the electrodes are separated by air gaps at the work engaging face, rather than by solid dielectric material.

Further objects are to provide an improved form of electrode pressure member particularly adapted for the lsetting of long rectangular 2 patches, and to provide an improved mounting arrangement and actuating mechanism for a high frequency patch press.

The characteristic feature of the invention is a pressure member having the necessary insulating material for the electrodes spaced from the work surface, and having a pressure face consisting of bare electrode elements which contact the work surface directly and apply the necessary mechanical pressure to the top of the patch. The electrodes preferably comprise parallel feet of different polarity extending across the patch to establish a plurality of dielectric fields over small sub-areas covering the patch.

4 In the case of a rectangular patch having square ends, it is preferred to direct the work engaging feet of the electrodes at an angle of 45 degrees with respect to the sides of the patch to insure uniform application of pressure and heat at both ends of the patch.

The invention will be better understood and still further objects and advantages will become apparent from the following description of the different embodiments illustrated in the accompanying drawings. Various changes may be made in the construction and arrangement of parts and certain features may be used without others Without departing from the spirit of the invention as defined in the appended claim-s, it being understood that the drawings are intended merely to illustrate the principles of the invention and not to limit the invention.

In t-he drawings:

Figure l is a side elevation view, with parts in section, showing a plywood patch press embodying the principles of the invention;

Figure 2 is a View taken on the line 2 2 of Figure 1;

Figure 3 isa perspective view, partly in section, of a plywood panel containing a sled patch;

Figure 4 is an enlarged perspective View 0f the electrodes shown in Figure 1;

Figure 5 is a sectional plan view of a modification having diagonal electrode feet;

Figure 6 is a top plan view of another modication, with parts broken away, showing a different electrode arrangement; and

Figure 7 is an end elevation view of the embodiment shown in Figure 6.

Referring now to the general view in Figure 1, the numeral I0 designates a table for supporting a plywood panel W having a patch P to be glued in place. The numerals Il and I la designate electrodes of opposite polarity which comprise a heating and pressure member for furnishing the heat and pressure necessary to glue the patch P to the panel. The two electrodes il and Ha are connected at one end by short flexible leads l2 and I3 to coaxial conductors I4 and l5 which extend back to a suitable high frequency generator G. The numeral I6 designates a small inductance mounted on the opposite ends of the electrodes to tune the circuit, This inductance may not be required if the electrical properties of the head are such as to match the load to the high frequency generator.

The electrodes i l and i la are secured by screws il to the under side of a heavy rigid block of dielectric insulating materialv 2i). The heads of screws Il are conventionalized in Figure 1, but it is understood that in practice the screw heads are either flat or rounded, and are countversunk so as to be substantially flush with the electrode surface to avoid projecting corners which would produce corona and brush discharge effects. The block of dielectric material 2@ is secured to a metallic plate 2| by means of screws 22 which are positioned remotely from the nearest screws lll. Plate 2l is mounted on the lower end of a plunger 23 4which is carried by a piston rod 245 e extending from a piston in a double acting air cylinder 25.

Numerals 2.5 and 2 indicate air supply and exhaust pipes for opposite ends or" the cylinder 25. These pipes are connected through conventional reversing valve mechanism `with a suitable compressed air supply for lowering and raising the piston rod. When compressed air is admitted to the cylinder above the piston through pipe Z and the air under the piston is allowed to exhaust through pipe 2l, the piston is driven downwardly in the cylinder with considerable force. When compressed air is admitted through pipe 2 to the Vcylinder beneath the piston and pipe 25 is opened to exhaust, the piston is raised in the cylinder and the various parts of the apparatus assume the positions shown.

The upper-end of plunger 23 is mounted for sliding movement in a bore 28 in the piston rod 2d. The lower end lof the piston rod is equipped with a iange 29 having studs 3l with adjustable stop nuts 3o to limit the movement of plunger `23 relative to the piston rod. A stop plate 32 on plunger 23 has holes loosely tting the studs 3i whereby plunger 23 is lifted by nuts 30 on the upward stroke of vpiston 24 and pressed downwardly by iiange 29 on the downward stroke of the piston. The nuts lSii are backed off on the studs 3| to a greater distance from the flange 29 than the thickness of plate 32 to allow a certain amount oflost motion. Plunger 23 is urged downwardly relative to the piston rod by spring 33.

Also mounted on ange 2Q is a' bracket Sii carrying a switch 35 to control the energization of the electrodes El andlla. Switch k35i has an actuating button 35 positioned to be depressed by the plate 32 when the flange 22 engages said plate. The switch is normally open to deenergize the electrodes when the parts are in nonworking position as shown in Figure l. Air pressure in pipe 21 then holds the piston rod 2d in its upper position supporting the electrodes at a distance above the vtop of table l@ by the engagement of lnuts 30 with the underside of plate 32 and button 36 is not engaged by the plate 32. With the pressure member thus raisedga panel W-having the patch P is moved across the table l to a'position placing the patch underV the electrodes or the pressure member, as shown. It is understood that the patch P has previously been coated with thermosetting glue on its underside and placed in position in a defect removal opening or recess in the top face oi the panel which exactly ts the patch.

The patching machine is equipped to perform automatically all the operations necessary to secure the patch after it has been placed in position as shown in Figure 1, but it wiil be understood that only those parts of the machine necessary to an understanding of the present invention are illustrated. The machine is placed in operation by admitting compressed air to the pipe 26 and opening the pipe 2i to exhaust, thereby causing the piston rod 2li to be driven downwardly, lowering the electrodes toward the work. As soon as the electrodes rest upon the work, flange 29 moves downwardly against stop plate 32, causing switch button 3S to engage this plate and close switch 35, to energize the electrodes. Thus, the heating cycle is started concurrently with the application oi pressure to the patch.

It will be understood by persons skilled in the art that when the velectrodes l l and lla are thus energized, high frequency dielectric elds are set up between the electrodes to produce stray field heating of the thermosetting glue on the underside of the patch. The glue is heated more quickly than the surrounding wood, and, with the application of sumcient electrical energy, it is set in a matter of a few seconds while the patch is held iirmly in place by the electrodes on the pressure member.

The operation may be terminated manually, but preferably by a suitable time control mechanism (not shown) connected with the mentioned air valve to reverse the connections to pipes 2%'3 and 2i. When air pressure is admitted to pipe 2,7 .and pipe 26 is opened to exhaust, piston rod 2d is raised. As the piston rod starts to move upwardly iiange 2@ draws away from plate 32 to release the switch button 36 and allow switch 35 to open, deenergizing the electrodes and terminating the heating cycle. Nuts 35 engage the underside of the plate 32 to raise the pressure member back to its Figure 1 position so that the patched panel can be removed.

Figure 1 also does not show the usual movable guard cage around the pressure member to preA vent the operator from coming into contact with the electrical conductors while they are energized.

Figure 3 is an enlarged broken away view illustrating a sled patch applied to a plywood panel to eliminate a defect in the top veneer of the panel. The panel is prepared for patching by routing out the defect in the vface veneer il of the three-ply panel W which comprises the three sheets of veneer di, 42 and d3. The routing operation to remove the defect is carried down to the glue line between veneers il and 112, and is comned to an outline corresponding to the size and shape of the prepared patch P. The veneers in a plywood panel are frequently of different thickness, the face veneer di being the thinnest, which places the glue line on the patch relatively close to the top surface which is engaged by the electrodes and in-an eiiective position for'stray field heating.v in boards and lum,u ber the routing is carried down to a depth equal to the thickness of the patch to be applied.`

The electrode pressure member of the present invention may beused with any form of con# Ventional patch such as a' circular patch, an oval patch, an elongated round end patch, or a boatshaped patch, but the sled patch illustrated in Figure 3 is particularly well suited for patching the face sheets of plywood panels. The sled patch P has parallel sides 44 running with the grain, and square cut end lines 45. The name sled patch derives from the fact that the ends taper in thickness in a curve 45 which is tangent to the bottom surface of the patch and substantially intersects the top surface of the patch at the end line 45. Thus, the glue line on the bottom of the-patch is brought to the surface of the panel at both ends of the patch in long sweeping curves which correspond in general to the curvature of the stray eld beneath the electrodes, so that the stray fields in the glue line at the ends of the patch become practically a vpart of the main eld, thereby increasing the heating effect in the glue and reducing the heating of the wood. The side edges 44 of the patch are also inclined but at a much steeper angle than the end surfaces 46 and are flat, edge grain surfaces. End surfaces 4B have a maximum of flat grain and a minimum of end grain, which enhances the strength of the bond at the ends of the patch.

The electrodes and Ila, shown in perspective in Figure 4, are identical castings made from a non-corrodible metal such as bronze. Each electrode has a top bar 5l rigidly secured to the flat underside of the insulating block by means of screws I'I. Depending from the bar 5| are a plurality of Vertical legs 52 having parallel feet 53 extending horizontally in a lateral direction. The feet 53 have fiat work engaging surfaces 55 on their undersides disposed in a common plane parallel with the underside of insulating block 20. The two electrodes Il and ||a are mounted on the block 20 with the feet 53 oppositely directed and equally spaced to provide a series of island work engaging surfaces at a considerable distance from the dielectric material. The bars 5| and legs 52 of the two electrodes are considerably farther apart than the spacing of the feet 53, and so, when the electrodes are connected to a suitable source of high frequency electrical energy, a strong alternating dielectric field is established between the feet 53 substantially in the plane of the Work engaging surfaces 55, and the stray field through the glue line on the bottom of a thin veneer patch is relatively close to the plane of surfaces 55 when these surfaces are pressed down upon the top of the patch.

The glue spread on the patch should be controlled so that a minimum of excess glue will be squeezed out around the margin of the patch, but, even if some of the wet glue does come into contact with the bare electrodes, it does not interfere materially with the heating of the main film of glue on the bottom of the patch. Such glue as may be squeezed out does not come in contact with the dielectric block 20, and ample spacing and ventilation are provided between the block 20 and the work surface so that in any event the dielectric material does not become heated from the work. Under the worst conditions, some wet glue along an edge of the patch, or a smear of wet glue on top of the work surface, might bridge the gap between a pair of the electrode feet to cause a momentary flashover, but when this happens the head can be raised, the excess burnt glue scraped off the panel and the head again lowered to continue the heating without harming the block 2|] to any extent.

Figure 5 shows a sectional view of a modified electrode arrangement, taken on a horizontal plane intermediate between the work engaging surfaces of the electrodes and the dielectric block on which they are mounted. In this embodiment, the two electrodes 60 and 6| take the same form as the electrodes and Ila in Figure 4 except that the legs 62 and feet B3 are directed at an angle of approximately 45 degrees to the longitudinal direction of the patch P and bars 5|. The angular disposition of the feet 63 in Figure 5 insures more uniform application of heat and pressure at the ends of a rectangular patch than lwould necessarily be obtained with the embodiment shown in Figure 4 where the two ends of the patch might be spaced differently from the nearest electrode foot. In Figure 5 it will be seen that at least one of the feet 63 will always lie across an end line 45 to hold it down flat without careful positioning of the panel under the tool.

The types of electrode pressure member shown in Figures 4 and 5 are used on patches considerably shorter than the pressure member as exemplied by the patch P in Figure 5, and also on long patches which require two or more applications of the pressure member to treat the whole length of the patch. When the patch is longer than the pressure member, the pressure member is first applied to one end of the patch and then the panel is shifted longitudinally of the patch and the pressure member applied again, over the other end of the patch. This style of patch is particularly convenient in view of the fact that most defects in wood extend along the grain in such a manner that a long defect does not require any wider patch than a small defect. The sled type patch and the present electrode arrangement thus allow the patches to be made in different lengths, all having the same width, so that the largest and smallest patches may be set with the same equipment. Heretofore, the conventional shapes of the patches have required different heat and pressure tools for different sizes of patches.

Figures 6 and 7 show an electrode arrangement for use with a three wire push-pull circuit or Iby proper connections used in the conventional two wire or coaxial line circuit. The two electrodes 'Il are connected to one circuit wire, the electrodes |2 to another circuit wire, and the electrodes '|3 to the third, or neutral, circuit conductor which may be grounded to the pressure member of the machine. For use on the conventional two wire circuit or coaxial line circuit the four electrodes and i2 are connected electrically and connected to one line and the electrodes 13 are connected electrically and connected to the other line.

In this embodiment, the four electrodes '|I and 'I2 are mounted in a rigid dielectric member 15, and the intervening electrodes 'I3 are mounted in a top plate 'I6 which is secured to the piston rod of a fluid pressure cylinder to apply the necessary pressure to all the electrodes. Electrodes 13 are T-shaped and have vertical legs 11 secured in the plate '|6. In an installation and circuit where it is feasible to ground the third wire to the piston rod or plunger 23, the plate 16 may be a metal plate in electrical contact with plate 2|, but the plate 16 may also be an insulating block similar to the dielectric block 20 in Figures 1 and 4, the upright legs of the electrode 13 then being connected together by a suitable bus bar or other common conductor.

The lower extremities of all the electrodes in Figures 6 and '7 are disposed in a common horizontal plane to present the effect of a flat pressure face in engagement with the work surface, as shown. Each electrode thereby presents an island work engaging surface against the patch B, remote from the dielectric supporting material. The work surface, electrodes and dielectric material l5 are well ventilated as in the Figure 4 and Figure 5 embodiments.

The work engaging feet of the electrodes in Figure 6 are of different lengths to cover an oval area slightly larger than the conventional boatshaped patch B, but the same general electrode arrangement may obviously be adapted to circular patches, round ended long patches, and the present sled patch P. It will also be apparent to persons skilled in the art that the electrodes may be turned to diagonal positions as in Figure 5 and that they may be limited to three in number and disposed longitudinally instead of transversely of the patch, if desired.

Thus, the dierent embodiments illustrate a Variety of bare electrode patch pressing tools wherein the electrodes themselves have air sep arated island work engaging portions to create the dielectric high frequency heating ield and to hold the patch in place While the glue under the patch is being heated to its thermosetting temperature. In each embodiment, the 'necessary dielectric support and pressure applying member is spaced above the work surface where it will not become heated nor smeared with glue from contact with the work. There is ample ventilation above the work surface to cool the electrodes and dielectric member and provide for the escape of steam from the wood and from the moisture in the wet glue. Still other electrode arrangements having these features and advantages will occur to persons skilled in the art, and all Vsuch additional modifications within the scope of the appended claims are included in the invention. The heat and pressure applying tool engages only the work surface which is to be patched and so relatively thick plywood and lumber may be treated with the same eciency as conventional thicknesses of plywood.

Having now described my invention and in what manner the same may be used, what I claim as new and desire to protect by Letters Patent is:

1. In a high frequency glue curing press, a pressure member having work engaging electrodesof different polarityadapted to be connected with a high frequency generator, a member for Inoving said pressure member toward and away from a work piece, a lost motion connection between said two members, and a switch controlling the energization of said electrodes mounted on one of said members and engageable with the other member for actuation by relative movement of the two members while said pressure member is in engagement with the work piece.

2. In a high frequency glue curing press for pressing a patch into a prepared recess in one surface of a wood panel and the like, a plurality of electrodes of different polarity having spaced parallel pressure feet constituting a rigid discontinuous pressure face arranged to engage the patch and extend over the edges thereof in contact with exposed glue lines at saidedges I'on said one surface of the panel, and a dielectric supporting and pressure applying member for said electrodes connected therewith spaccrd rela'- tion with said pressure feet, said pressure feet being otherwise separated from each other and from said supporting member by Ventilating air gaps communicating with atmosphere.

3.In a high frequency glue curing press for pressing a patch into a prepared recess in one surface of a wood panel and the like wherein said patch and recess have glue lines exposed on said surface around the edges of the patch, a table for supporting said panel with said one surface uppermost, a dielectric member mounted iormovement toward and away from said surface, electrodes of different polarity mounted on said member, and work engaging pressure feet on said electrodes separated from each other and from said dielectric member by air gaps.

4. In a high frequency glue curing press for pressing a patch into a prepared opening in a sheet and wood veneer and the like whereby glue lines around the edgesk of the patch are exposed on the face of the sheet, a dielectric block, electrodes of different polarity mounted on said block, and pressure feet on said electrodes having legs extending outwardly from said block, said pressure feet being otherwise separated from each other and from said block by ventilating and insulating air gaps and said feet being arranged to engage the surface of said patch and extend over said exposed'glue lines to press all parts of the patchiirmly in place.

5.`In a high frequency wood patch press, a stray field type heating and pressing member adapted to engage the face surface of a veneer patch and the like and extend over the edges yof the patch in contact with exposed glue lines at the edges of the patch, said member comprising a dielectric block and a pair of electrodes of different polarity, said electrodes having Aelongated base portions mounted'on said block, and oppositely directed interdigital work engaging pres sure feet extending outwardly from saidbase portions of `the electrodes but otherwise separated from each other and from said block by Ventilating and insulating air gaps.

6. I n ya high frequency wood patch press, a stray eld type heating and pressing member adapted to engage theface surface of a veneer patch and the like and extend over all the edges of the patch in contact with exposed glue lines at the edges of the patch, said member comprising a dielectric block and a pair of electrodes oi rdiiferent polarity, said electrodes having elongated base portions mounted on said block in parallel relation, and oppositely directed parallel interdigital work engaging pressure feet offset outwardly from said base portions of the electrodes andv extending at oblique angles relative thereto, lsaid pressure feet being otherwise separated from each other and from said block by Ventilating and insulating air gaps.

7. A high frequency heating and pressing unit for relatively stationary application to one surface of a workpiece such as wood veneer and the like comprising, a rigid dielectric member relatively. movable toward and away from said surface, rigid electrodes of difierent polarity mounted on said member, and rigid feet on said electrodes outstanding from said dielectric member and arranged to constitute a discontinuous pressure face to zengage Iand apply substantial pressure to said one surface of the work piece in a heating cycle, said electrode feet being separated from each other and from said dielectric .member by ventilating air gaps communicating of wood veneer and the like whereby glue lines around the edges of the patch are exposed on the face of the sheet comprising, a table for supporting said sheet with said face uppermost, a rigid dielectric member, a uid pressure operated unit connected with said dielectric member for moving said dielectric member relatively toward and away from said table, electrodes of diiierent polarity mounted on said dielectric member, and rigid outstanding work engaging pressure feet on said electrodes separated from each other and from said dielectric member by Ventilating air gaps communicating with atmosphere.

9. A high frequency glue curing press for pressing a patch into a prepared opening in a sheet of wood veneer and the like whereby glue lines around the edges of the patch are exposed on the face of the sheet comprising, a table for supporting said sheet with said face uppermost, a pressure applying member having a rigid dielectric element, a uid pressure operated member for moving said pressure applying member and dielectric element relatively toward and away from said table, electrodes of diferent polarity mounted on said dielectric element, work 10 engaging pressure feet on said electrodes separated from each other and from said dielectric element by air gaps communicating with atmosphere, a lost motion connection between said two members, and a switch controlling the energization of said electrodes mounted on one of said members and engageable with the other member for actuation by relative movement of the two members While said pressure feet are in engagement with the sheet.

HARRELL RENN.

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